1. Field of the Invention
This invention relates in general to magnetic transducers for reading information signals from a magnetic medium and, in particular, to an improved magnetoresistive read transducer.
2. Description of the Invention
The prior art discloses a magnetic transducer referred to as a magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at great linear densities. An MR sensor detects magnetic field signals through the resistance changes of a read element made from a magnetic material as a function of the amount and direction of magnetic flux being sensed by the element. These prior art MR sensors operate on the basis of the anisotropic magnetoresistive (AMR) effect in which a component of the resistance varies as cos.sup.2 of the angle between the magnetization and the direction of current flow. These MR sensors have operated on the basis of the AMR effect even though this effect produced only a very small percentage change in the resistance.
More recently, reports have been published of techniques for obtaining enhanced MR effects. One of these publications, "Enhanced Magnetoresistance in Layered Magnetic Structures with Antiferromagnetic Interlayer Exchange", G. Binasch et al., Phys. Rev. B. V39, p. 4828 (1989) and U.S. Pat. No. 4,949,039 describe a layered magnetic structure which yields enhanced MR effects caused by antiparallel alignment of the magnetization. However the saturation fields required to obtain these changes in resistance were too high and the effect too nonlinear and therefore unsuitable for producing a practical MR sensor.
In order for the MR phenomena in multilayered structures to be of technological importance, it is necessary to achieve large changes in resistance at relatively low saturation fields, so that the rate of change of MR vs. applied field can be optimized.